This paper examines the temporal variability of airborne emissions of ammonia from livestock operations and fertilizer application and nitric oxide from soils. In the United States, the livestock operations and fertilizer application categories comprise the majority of the ammonia emissions inventory. Air quality modeling efforts for the most part, however, have assumed annual-average ammonia emission factors. Based on a literature review, we have generated crude seasonal adjustments of ammonia emissions taking into account climatic factors, manure spreading, and fertilizer application schedules. Nitric oxide (NO) emissions from soils estimated with the Biogenic Emissions Inventory System (BEIS2) comprise about 10% of total annual nitric oxide emissions across the United States. BEIS2 distributes emissions by land use and modulates emissions based on hourly soil temperature, with the highest emissions arising from fertilized soils during warm conditions. A new algorithm has been developed that incorporates daily rainfall patterns, fertilizer application schedules, and plant canopy growth. Simulations with this new algorithm show more short-term variability and an overall reduction in soil NO emissions compared to the BEIS2 algorithm, particularly in the midwestern United States. The techniques introduced for estimating the temporal variability of ammonia and nitric oxide emissions from agricultural operations may help improve the accuracy of fine particulate and ozone models.
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